TXA.sub.2 discovered by Samuelsson et al. in 1975 has a strong platelet aggregation activity as well as vascular smooth muscle-contracting activity and bronchial smooth muscle-contracting activity (Proc. Natl. Acad. Sci. U.S.A., 72, 2994 (1975)). On the other hand, plastaglandin I.sub.2 (PGI.sub.2) is known as a compound having activities opposite to the above-mentioned activities, that is, as a compound having a strong platelet aggregation inhibiting activity and vasodilation activity (Nature, 263, 663(1976)). Since these two compounds are synthesized from arachidonic acid in the body and since their activities are strong, it is said that the balance between TXA.sub.2 and PGI.sub.2 is important for keeping the homeostasis of circulatory system. Therefore, if this balance is inclined to the side of TXA.sub.2, activation of platelets and subsequent thrombus formation and vasoconstriction are caused, which is thought to be a cause of circulatory disorders including ischemic heart diseases such as angina pectoris and myocardial infarction, cerebrovascular diseases, renal disorders and the like. Further, since TXA.sub.2 has a strong bronchial smooth muscle-contracting activity, it is thought that TXA.sub.2 also has a relationship to bronchial asthma. Thus, inhibition of activities of TXA.sub.2 is thought to be effective for therapies of circulatory disorders including ischemic heart diseases such as angina pectoris and myocardial infarction, cerebrovascular diseases and renal disorders, as well as bronchial asthma. So far, as the drugs to inhibit the activities of TXA.sub.2, a TXA.sub.2 receptor antagonist (Circulation, 81, Suppl. I, I-69(1990); Medicinal Research Reviews, 11, 503(1991)), and an inhibitor of TXA.sub.2 synthetase have been reported.
However, no drugs which sufficiently inhibit the activities of TXA.sub.2 have been obtained yet.